Steering arrangement

ABSTRACT

The invention concerns a steering arrangement ( 1 ) with a steering handwheel ( 2 ), which is unrotatably connected with a steering sensor, and with a wheel ( 3 ) steered by a steering drive ( 4 ) without a mechanically active connection between steering handwheel ( 2 ) and steered wheel ( 3 ). In this steering arrangement a simple way of realizing a counter action of the steered wheel on the steering handwheel ( 2 ) is wanted. For this purpose the steering sensor is made as an electrical machine ( 6 ), which works as a generator, for the production of a steering signal and is connected with a switching device ( 9 ), whose load behavior is variable.

The invention concerns a steering arrangement with a steering handwheel,which is unrotatably connected with a steering sensor, and with a wheelsteered by a steering drive without a mechanically active connectionbetween steering handwheel and steered wheel.

An arrangement of this kind is known from DE 42 07 719 A1. The steeringangle, which is transmitted from the steering handwheel via a steeringshaft to the steering sensor, is used to control the opening of ahydraulic valve so that a hydraulic motor can steer wheels in onedirection or the other. To give the operator a sense of the steeringbehavior, a counter-action motor is provided, which also acts upon thesteering shaft.

The steering arrangement of the present invention is primarily used withdriven machines, like, for example, fork lift trucks or forestrymachines. In the course of one working day such machines perform manysimilar movements, for example, when a fork lift truck collects andpiles up palettes. In order to optimize the movement processes for theoperator ergonomically, so-called mini steering wheels have beenintroduced. Such a mini steering wheel is known from the Swedish patentSE 466 099. Also in connection with these mini steering wheels acounter-action is desired. However, the advantage of a compact designoffered by the mini steering wheel should be maintained, even with thecounter-action measures.

The task of the invention is to provide a simple method of managing acounter-action.

In a steering arrangement of the kind mentioned in the introduction,this task is solved in that the steering sensor is made as an electricalmachine, working as a generator, for the production of a steering signaland is connected with a switching device, whose load behavior isvariable.

This measure provides a relatively simple way of obtaining both thesteering signal, that is the desired value specified by the steeringhandwheel, which must be followed by the steered wheel(s), and acounter-action with which the user “feels” the resistance to be overcomeby the steered wheel. The steering signal is simply produced by anelectrical machine working as a generator. By means of the voltageproduced by the electrical machine working as a generator and the timeit takes to produce the voltage both the steering speed and the steeringangle can be calculated. However, the driving of a generator requires atorque, which again depends on the electric load, which must be servedby the generator. An illustrative example of such a load is an ohmicresistor, which is connected with the output terminals of the generator.The smaller this resistor is, the larger is the torque required to drivethe generator. A change of the electrical resistance thus enables achange of the torque to be produced by the user or operator. Of coursethere is a number of other opportunities of influencing the “loadbehavior”. Instead of an ohmic resistor, commonly known electronic orelectrical switching elements can be used, which change the current flowbetween the generator terminals. For example, a keyed switch can beused, whose keying interval can be adjusted. It is also possible toproduce a counter-voltage and then feed it to the generator terminals.If, for example, the counter-voltage is larger than the generator outputvoltage, the user must work against a motor to turn the steeringhandwheel. This enables a feedback to the driver or user. With thisembodiment one single mechanical element is sufficient, namely theelectrical machine. An electrical machine of this kind is relativelycompact, so that the advantage of a good space utilization ismaintained. The combination of signal production with the opportunity ofa counter-action gives a very narrow coupling between the two measures,so that major errors caused by different operational behaviors inconnection with the production of steering signals and the counteraction can be avoided. of course, the size and the performance of thesteering handwheel and the electrical machine must be adapted to eachother. A small steering handwheel only requires a small machine. Thecounter-torque or braking-torque can be changed in dependence of variousparameters, for example, vehicle speed, vehicle load or time of day.

Preferably, a transmission is arranged between the steering handwheeland the steering sensor. This transmission causes that the electricalmachine turns substantially faster than the steering handwheel. Forexample, a transmission ratio of 5:1 can be assumed. In this case twoadvantages are obtained. Firstly, a stronger steering signal isachieved, as with a higher speed the generator supplies a strongervoltage signal. Secondly, the counter-action torque of the electricalmachine on the steering handwheel is accordingly amplified.

Advantageously, the steering handwheel is made as a mini steering wheel,and the transmission is integrated in the mini steering wheel. With amini steering wheel no large torques have to be transmitted. The onlyrequirement is that the driver must get a feeling for the steeringbehavior. In this case it is also sufficient to have an accordinglysmall or weakly dimensioned gear, which can be incorporated in the ministeering wheel. This means that only very little additional space isrequired for the gear.

In an alternative embodiment the transmission can be fitted on theoutside of the electrical machine. As mentioned above, the transmissionis a relatively small component, and the additional space required ishardly mentionable.

Advantageously, the steering handwheel is supported in a housing, inwhich the electrical machine and at least one part of the switchingdevice influencing the torque are arranged, the switching device havinga BUS connection. The BUS connection can, for example, be configured fora CANBUS. Exactly within the vehicle sector the CAN-BUS is very muchused as BUS. By means of this CAN-BUS the required information can betransmitted from the steering handwheel to the steering drive and viceversa. It is also relatively simple to introduce additional signals,whose production devices will be described below.

Advantageously, the electrical machine can be driven as a motor. In manycases, electrical machines can be driven both as generators and asmotors. When, in the present case, the electrical machine can be drivenas a motor, additional opportunities occur, for example, the torque feltby the user can be increased. The motor function can also be used forother purposes.

Preferably, a torque sensor connected with the switching device isarranged on the steered wheel, and the switching device adjusts its loadbehavior in dependence of the output signal of the torque sensor. Thus,the forces influenced by the steered wheel can be simulated.Particularly, forces can be passed on to the steering handwheel, whichact upon the steered wheel from the outside. The operator or driver thengets an even better feeling of the steering behavior of his vehicle. Forexample, he learns via the steering handwheel, when the steered wheelmeets a resistance. By means of the torque sensor it can also bedetected when the steered wheel reaches its end stop. This keeps thewear at a minimum or prevents damages.

In an advantageous embodiment the steered wheel has an end-stop sensingdevice connected with the switching device, and the switching deviceproduces an irregular torque at the electrical machine, when the steeredwheel reaches a movement limit. Then the operator will be informed thatthe steered wheel has reached its end stop, for example in that positionthe steering wheel vibrates or is exposed to a pulsating torque. Thus,an oversteering of the steering arrangement is prevented. The torque canbe produced by a motor or be a varying resistance torque.

Preferably, the steered wheel is provided with a position sensorconnected with the switching device, the. switching device returning thesteered wheel to a neutral position. This may, for example, happen, whenthe steering handwheel does not move for a predetermined period. Thisgives an automatic return of the vehicle to the straight-forwardposition, whenever required.

In this connection it is advantageous if the switching device triggersthe electrical machine synchronously with the steered wheel. Then theuser simultaneously gets the information that the steered wheel is movedback to the neutral position. This enables him to interrupt thismovement by an operation of the steering handwheel, for example byholding it. If he does not, the steering handwheel will also be in theneutral position at the end of the returning process. If desired, thisprocedure can be limited to standstill periods of the vehicle.

In a preferred embodiment it is provided that the switching devicecompares the steering handwheel position with the steered wheel positionand adjusts the torque on the steering handwheel in dependence of thedifference. Thus, for example, the steering handwheel acceleration canbe influenced so that the steering handwheel cannot be turned fasterthan for the steered wheel to follow. When there is a large deviationbetween the two positions, for example, the steering handwheel is farahead of the steered wheel. When then the torque is increased, which theoperator must overcome, the steered wheel has the opportunity ofcatching up again.

Advantageously, the steering handwheel has a marking, and an additionalstationary marking is provided in the steering handwheel surroundings,the switching device trigging the electrical machine to work as a motor,in a way that the relative position of the two markings corresponds tothe angle position of the steered wheel. For example, when the steeringsystem is used in a fork lift truck, it is important to know in whichposition the steered wheel is, particularly when the operator comes backand starts the vehicle again after having been away. For this purpose itis known to provide some sort of graphic representation of the wheelpositions. However, advantageously, this position statement can also berealized via the steering handwheel, particularly when the steeringhandwheel is made as a mini steering wheel. As it is possible to actupon and adjust the angle position of the steering handwheel by means ofthe electrical machine working as a motor, it can be imagined that theposition of the steering handwheel is adapted to the position of thesteered wheel, each time the vehicle stands still and the steeringhandwheel is not operated for a predetermined time. For this purpose,the angle position of the steering handwheel needs not be particularlyaccurate, as the crucial thing is to give the operator a feeling of theposition of the steered wheel.

In the following the invention is described on the basis of preferredembodiments in connection with the drawings, showing:

FIG. 1 a schematic circuit diagram for description of the steeringarrangement

FIG. 2 a schematic side view of a mini steering wheel

FIG. 3 a view III—III according to FIG. 2

FIG. 4 an additional embodiment of a mini steering wheel

FIG. 5 a schematic view of a device in the steering arrangement

A steering arrangement 1 has a steering handwheel 2 and a steered wheel3. A steering drive 4 is provided for the operation of the steered wheel3. The steering drive 4 is only shown schematically. It could be ahydraulic motor with corresponding operating valves, an electrical motorwith corresponding wiring or another power producing device.

The steering handwheel 2 is connected with an electrical machine 6 via agear 5. The electrical machine can be a DC-machine, an AC-machine or athree-phase field machine. In the present case it is merely importantthat it can work both as a generator and as a motor. The machine shownis a DC-machine, which has the advantage that the voltage available ator produced by its terminals 7, 8 contains information about therotation direction of the machine 6.

The electrical machine 6 is connected with a switching device 9. Thisswitching device has two tasks. Firstly, it comprises a device 10 fordetecting the voltage at the terminals 7, 8 and for evaluation of thisvoltage. In the “undisturbed” state, the rotation speed of the steeringhandwheel can be calculated by means of the terminal voltage, ifrequired transmitted by the gear 5. The higher the speed, the higher thevoltage produced by the electrical machine 6 when operated as agenerator. By means of a simple integration information about therotation angle travelled by the steering handwheel 2 can be obtained.

The gear 5 has a gear ratio higher than 1, for example 5:1. In this caseone rotation of the steering handwheel 2 causes five rotations of theelectrical machine 6, which involves the advantage that due to thehigher rotation speed of the electrical machine 6, the voltage inducedis also higher. Of course, the gear ratio must be considered whenevaluating the terminal voltage.

The switching device 9 also comprises an additional device 11 by meansof which the load behavior of the switching device can be changed. Thisis shown schematically by a variable resistor 12. The smaller the valueof this ohmic resistor 12 is, the higher is the torque to be produced bythe operator to turn the steering handwheel 2. Thus, the torque to beproduced by the operator can be changed by the device 11. A “feedback”of the steering behavior of the steered wheel 3 on the steeringhandwheel 2 can be imitated or simulated by a change of the torque.

The ohmic resistor 12 was only chosen to provide a simple way of showingthe variation of the torque to be produced. Of course there is a numberof other ways of realizing the variations of the torque of theelectrical machine 6. For example, the voltage at the terminals 7, 8 canbe increased by means of the device 11, so that the operator must turnthe steering handwheel 2 against an operation of the electrical machine6 working as a motor. In this case, a reaction torque can be produced onthe steering handwheel 2, which is higher than the highest countertorque, which could be produced in the electrical machine 6 when used asa generator.

For a change of the “load behavior” of the switching device through thedevice 11, a control device 13 is provided, which is connected with aCAN-BUS 14. The communication from the switching device 9 to thesteering drive 4 takes place via the BUS 14. Further, the communicationfrom the sensors to the switching device 9 or the control device 13(described below), respectively, takes place via this BUS.

On the basis of the information from the device detecting the terminalvoltage the control device 13 controls the steering drive. As thevoltage at the terminals 7, 8 can be varied through the device 11 for achange of the load behavior of the switching device 9, the correspondinginformation must be considered when evaluating the terminal voltage. As,however, the setting of the “load behavior” takes place via the controldevice 13, the control device knows which changes it has effected, andcan accordingly consider these when detecting the control signals forthe steering drive 4. This is normally possible without problems, whenthe individual signals can be superimposed linearly, that is, in alinear superposition. Also in connection with a non-linear behavior therequired information can be obtained from the terminal voltage, when thenon-linearity is known.

As mentioned, various sensors are arranged on the steering drive 4. Oneof them is a torque sensor 15. The torque sensor detects the torqueacting upon the steered wheel 3 and reports it back to the controldevice 13 of the switching device 9. The switching device 9 can thenadapt its load behavior to the detected torque. “Load behavior” does notonly mean a passive reaction. When, for example, the steered wheel meetsa hindrance, it is possible that the switching device 9 increases theterminal voltage to expose the steering handwheel 2 to a correspondingmotor torque against the power of the operator. This corresponds to theblow, which a steering handwheel connected mechanically with the steeredwheels feeds back to the operator, when the steered wheel hits a borderstone or the like.

Further, an endstop sensor 16 for both directions of the steered wheel 3is arranged on the steering drive 4. The endstop sensor 16 detects, whenthe steered wheel 3 reaches its movement limit. When the switchingdevice 9 receives this information, the voltage at the terminals 7, 8 isacted upon in a way that the electrical machine 6 operates as a motorand produces a pulsating or vibrating movement of the steering handwheel2. For this purpose, for example, the voltage at the terminals 7, 8 isset to be periodically positive and negative. Thus, the operator getsthe information that the steered wheel is at the endstop, and that afurther turning of the steering handwheel 3 is pointless or evendangerous.

Finally, an additional position sensor 17 can be arranged on thesteering drive 4, which provides information about the angle position ofthe steered wheel 3. Of course, the position sensor can also take overthe function of the endstop sensor 16. The position sensor 17 is alsoconnected with the switching device 9 via the BUS 14. Now it can beprovided that the switching device 9 or the control device 13,respectively, returns the steered wheel 3 to a neutral position, whenthe steering handwheel 2 has not moved for a predetermined period. Ifrequired, it can be provided that this returning only occurs, when thevehicle stands still. For this purpose, a speed sensor (not shown) isprovided. For the returning the electrical machine 6 can then beoperated as a motor, so that the steering handwheel 2 follows themovement of the steered wheel, that is, a conformance between the anglepositions of the steering handwheel 2 and the steered wheel 3 ismaintained.

The steering arrangement 1 can also be used to obtain a limitation ofthe steering handwheel acceleration. Thus, it must not be possible toturn the steering handwheel 2 faster than for the steered wheel 3 tofollow. For this purpose, it is possible, as shown in FIG. 5, to detectthe steering handwheel angle ø, that is the position of the steeringhandwheel 2, which is passed on to the steering drive 4 as desiredvalue. Via the steering drive 4 the actual position I of the steeredwheel 3 can be detected. When now the desired value ø exceeds the actualvalue I by a constant value C, a corresponding counter torque M isproduced by the electrical machine 6 and passed on to the steeringhandwheel 2. In the embodiment in FIG. 5, the steering drive 4 isconnected with the steered wheel 3 via a toothed belt 27.

As shown in FIG. 1, the steering handwheel 2 has a marking 18. On thehousing 19, in which the steering handwheel is supported, there is anadditional marking 20. The position of the steered wheel is detected bymeans of the position sensor 17. When the vehicle stands still, theelectrical machine 6, which is for this purpose operated as a motor, canbe used to set the steering handwheel 2 so that the relative position ofthe two markings 18, 20 corresponds to the angle position of the steeredwheel 3. This gives the operator a visual information about the angleposition of the steered wheel 3, without requiring that he sees thesteered wheel 3. Such information is, for example, useful, when theoperator leaves the vehicle and returns after a while, or when anotheroperator takes over the vehicle.

There are different opportunities of realizing the steering handwheel 2,which are shown in the FIGS. 2 to 4. The steering handwheel 2 shown inFIG. 2 is made as a mini steering wheel. As shown in FIG. 3, thesteering handwheel 2 is rotatably arranged on a rotating shaft 21. Alsoa gear wheel 22 is supported on this rotating shaft 21, which gear wheelmeshes with an additional gear wheel 23. The gear wheel 22 isunrotatably connected with the electrical machine 6. On its radialinside the steering handwheel 2 has a toothing 24, which co-operateswith gear wheels 22, 23 in the way of a planet gear. With thisembodiment, which can be extremely compact, a gear ratio of, forexample, 5:1 can be obtained.

FIG. 4 shows an alternative embodiment, in which the gear 5 is fitted onthe outside of the motor 6. The steering handwheel 2, which may have amushroom shaped operating knob 25, which can also be used as marking 18,is connected with the gear 5 via a steering shaft 26. Also the completeswitching device 9 is comprised in the housing 19. Only the BUS 14 isled to the outside.

What is claimed is:
 1. Steering arrangement comprising a steeringhandwheel mechanically connected to a steering sensor, and having awheel steered by a steering drive without a mechanically activeconnection between the steering handwheel and the wheel, the steeringsensor comprising an electrical machine, working as a generator,producing a steering signal and being connected with a switching deviceproviding a variable load resistance to the steering handwheel so thattorque for driving the electrical machine when working as a generator ischanged in dependence on the load.
 2. Steering arrangement according toclaim 1, in which a transmission is located between the steeringhandwheel and the steering sensor.
 3. Steering arrangement according toclaim 2, in which the transmission is integrated in the steeringhandwheel.
 4. Steering arrangement according to claim 2, in which thetransmission is located adjacent to the electrical machine.
 5. Steeringarrangement according to claim 1, in which the steering handwheel issupported in a housing, in which the electrical machine and at least onepart of the switching device are located, the switching device having anelectrical connection to the steering drive.
 6. Steering arrangementaccording to claim 1, in which the electrical machine includes means todrive the electrical machine as a motor.
 7. Steering arrangementaccording to claims 1, including a torque sensor connected with theswitching device located proximate the steered wheel, the switchingdevice adjusting its variable load resistance in dependence of an outputsignal of the torque sensor.
 8. Steering arrangement according to claim1, in which the steered wheel has an endstop sensing device connectedwith the switching device, and the switching device produces anirregular signal to the electrical machine when the steered wheelreaches a movement limit.
 9. Steering arrangement according to claim 1,in which the steering drive includes a position sensor connected withthe switching device, the switching device including means responsive tothe position sensor to return the steered wheel to a neutral position.10. Steering arrangement according to claim 9, in which the switchingdevice includes means to activate the electrical machine synchronouslywith the steered wheel.
 11. Steering arrangement according to claim 1,in which the switching device compares the steering handwheel positionwith the steered wheel position and adjusts torque on the steeringhandwheel in dependence on the comparison.
 12. Steering arrangementaccording to claim 6, in which the steering handwheel has a marking, andan additional stationary marking is provided proximate the steeringhandwheel, the switching device including means to activate theelectrical machine to work as a motor, with a relative position of thetwo markings corresponding to an angle position of the wheel.